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Figure 1. Historical and predicted light source efficacies. Figure 2. 2010 version of Haitz’s Law.
new lighting paradigms. Developed by
Kodak 5 in the 1980s, OLED devices were
initially fabricated using vapor deposition
processes. The opportunity to use printing
processes for OLED fabrication opens up
new opportunities.
Presently, OLED efficacy is lower
than that for LED product, but is rapidly
increasing. It is too soon to know whether
OLED products will follow Haitz’s Law.
ssl assembly hierarchies
LED assembly
LED-based SSL assembly follows a 4 level
assembly hierarchy, Table 1.
LED assembly uses a broad range of
SMT processes and unique materials.
Following die singulation and lightemission
testing, binned die (based on
light quality) are assembled into a light
source. A Level 1 LED assembly is depicted
in Figure 3 6 . Ultimately, the light engine is
Figure 3. Level 1 LED package assembly.
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placed in a luminaire.
OLED assembly
In contrast to LED assembly, OLED
assembly follows a very different assembly
process, Table 2. While this is still a
four-level assembly hierarchy, Levels 0, 1
and 2 are merged into a comprehensive
assembly step since OLED fabrication
intrinsically produces the light source
(Level 0), and light engine (Level 1 and 2)
in an interrelated process, not as a series of
discrete assembly steps, which defines LED
SSL assembly.
This OLED assembly hierarchy
arises from the nature of the OLED
device, which is different from that for a
crystalline based LED. A typical OLED
light source fabricated on a glass substrate,
shown in Figure 4 7 , is composed of a
stack of thin films (usual total thickness
of 100-200 nm) situated between planar
Printed electronics for flexible solid-state lighting
electrodes, with at least one transparent
electrode to enable light to exit the OLED
structure. Descriptions of the various layers
are described in Table 3.
Visible light is created when electrons
and holes, driven by an applied voltage
across the electrodes, combine in the
OLED layers. A luminaire is formed when
the OLED is assembled into a structure
that protects the OLED from physical and
environmental damage as well as supplying
it with electrical energy and control
functions.
SSL OLED technology began as
a display technology. In addition to
developing the materials and fabrication
processes to produce displays, lithography
capable of sub-millimeter resolution was
also required for forming small pixels with
the OLED material sets. While requiring
similar OLED materials and substrates,
SSL requires lower resolution lithography
(i.e., the pixels are larger) so that a critical
display manufacturing step is removed
from the lighting path. The result is a
significant fraction of the manufacturing
cost is reduced for a luminaire relative to
a display, while concurrently increasing
manufacturing throughput and yields.
oleDs for solid-state lighting
As noted in the OLED assembly hierarchy,
Levels 0, 1 and 2 are strongly interrelated.
This interrelation is made more complex
by multiple options available for producing
the OLED device. These include:
• Vapor deposition vs. printed
processes
• Flexible substrate vs. rigid substrate
• Reel-to-reel (R2R) vs. sheet fed
processing
While some OLED material systems can be
Global SMT & Packaging Southeast Asia – Winter 2010 – 15